package com.jelly.io.nio.lock;

import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;

/**
 * 对映射文件部分内容加锁
 * 
 * @author Jelly
 * 
 */
public class LockingMappedFiles {
	static final int LENTTH = 0X8ffffff;
	static FileChannel fc;

	public static void main(String[] args) throws IOException {
		fc = new RandomAccessFile("test.data", "rw").getChannel();
		MappedByteBuffer out = fc
				.map(FileChannel.MapMode.READ_WRITE, 0, LENTTH);
		for (int i = 0; i < LENTTH; i++) {
			out.put((byte) 'x');
		}
		new LockAdnModify(out, 0, 0 + LENTTH / 3);
		new LockAdnModify(out, LENTTH / 2, LENTTH / 2 + LENTTH / 4);
	}

	private static class LockAdnModify extends Thread {
		private ByteBuffer buff;
		private int start, end;

		public LockAdnModify(ByteBuffer mbb, int start, int end) {
			this.start = start;
			this.end = end;
			mbb.limit(end);
			mbb.position(start);
			buff = mbb.slice();
			start();
		}

		@Override
		public void run() {
			try {
				FileLock fl = fc.lock(start, end, false);
				System.out.println("Locked: " + start + " to " + end);
				while (buff.position() < buff.limit() - 1) {
					buff.put((byte) (buff.get() + 1));
				}
				fl.release();
				System.out.println("Released: " + start + " to " + end);
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}
}
